Color-changing materials and multiple component materials having a color-changing composition

ABSTRACT

The present invention relates to a color-changing material and to a multiple-component material that includes a color-changing composition. The color-changing materials and color-changing compositions are capable of changing color in order to indicate a change in condition, such as a change in pH. The color-changing materials and color-changing compositions include a hydrogel-forming composition, a charged colorant and a pH adjuster. The hydrogel-forming composition includes at least one charged species.

FIELD OF THE INVENTION

The present invention relates to color-changing materials that include ahydrogel-forming composition, a charged colorant, a pH adjuster and asolvent. The hydrogel-forming composition includes either (1) a chargedhydrogel-forming polymer or (2) a neutral hydrogel-forming polymer andat least one of a charged polymer or a charged particle. The presentinvention also relates to multiple-component materials that include asubstrate and a hydrogel layer formed on the substrate. The hydrogellayer includes a color-changing composition. The color-changingcomposition can cause the hydrogel layer to change in appearance of itscolor when the hydrogel layer is exposed to a change in physical orchemical environment. For example, the hydrogel layer may be on anonwoven material that is used as a component of an absorbent article.The color-changing composition includes a hydrogel-forming composition,a charged colorant and a pH adjuster that changes color in response tothe presence of urine and water. Further, the present invention relatesto a method of printing on a substrate. The method includes the steps ofproviding a substrate to be printed upon and applying an ink materialonto the substrate. The ink material includes a hydrogel-formingcomposition, a charged colorant, a pH adjuster and a solvent.

BACKGROUND OF THE INVENTION

Many products, including consumer and professional products, are moreeffectively used by an end user when they include a feature thatindicates a particular condition or degree of use. An example of avisual indicator is a color indicator. Color indicators can eitherindicate a change in condition or a degree of use through a change from“no color” to “color” (or vice versa) or through a change from one colorto a different color.

Exemplary conditions that could be monitored using a color indicatorinclude physical conditions such as the presence of moisture andchemical conditions such as a change in pH. Exemplary consumer productsthat could be more effective and deliver more benefits to end users byincorporating a suitable color indicator include absorbent articles,facial tissues, bath tissue, paper towels, household cleaning items andpersonal cleaning wipes. Exemplary professional products that could bemore effective and deliver more benefits to end users by incorporating asuitable color indicator include products for medical use, safetygarments, industrial cleaning products and nonwoven materials.

Color indicators are well known and are available in various forms.Desirable performance attributes include durability and good retention(i.e. the color indicator remains where intended and does not leach outinto other components of the product within which it is being used).Depending on the product application, it may also be desirable to havethe structure in which the color indicator is used be wettable, butwater insoluble. For purposes of applying the color indicator to acomponent of a product, it may also be desirable to have a colorindicator that can be applied in liquid form at room temperature. Whenthe color indicator is in a liquid form at room temperature, the colorindicator can be printed (just like an ink composition) onto the desiredcomponent of a product.

Examples of how color indicators are already incorporated into consumerproducts include diapers that have wetness sensors. Some of the wetnesssensors used in diapers change color to indicate wetness while otherslose color in response to wetness (i.e. the color fades or disappearswhen it is dissolved by water). The concept of incorporating acolor-changing composition into a wearable article (such as a disposablediaper) is known in the art. For example, U.S. Pat. No. 7,159,532 issuedto Klofta et al. (hereinafter “the '532 patent”) is directed to wetnessindicating compositions having improved colorant retention anddurability for use with wearable articles. The wetness indicatingcompositions of the '532 patent have a first binding agent and a secondbinding agent. The first binding agent immobilizes a colorant when thecolorant is in its initial color state and the second binding agentimmobilizes the colorant when the colorant is in its final color state.The component materials used in the examples provided in the '532 patentare solid at room temperature as indicated by the description that theyneed to be melted in order to combine them. While the wetness indicatingcompositions of the '532 patent are capable of changing color inresponse to a stimulus, they are not capable of being applied to anarticle in liquid form at room temperature.

While the color-changing compositions known in the art provide certainbenefits, there remains a need for a film-forming composition that canbe applied to a substrate. There also remains a need for a compositionthat is durable, has good retention and that shows rapid and dramaticcolor change when the composition is used in a product. When the purposeof the composition is to detect the presence of wetness, there remains aneed for a composition that is wettable, but water-resistant andwater-insoluble. Further, there remains a need for a composition thatcan be applied, such as by printing, at room temperature so that thecomposition can be applied to a substrate without heating.

SUMMARY OF THE INVENTION

The present invention is directed to a color-changing material thatincludes a hydrogel-forming composition containing at least one chargedspecies, a charged colorant, a pH adjuster and a volatile solvent. Thehydrogel-forming composition is from 5 to 50% of the color-changingmaterial. The charged colorant is from 0.1 to 10% of the color-changingmaterial. The pH adjuster is from 0.001 to 10% of the color-changingmaterial and the volatile solvent is from 50 to 90% of thecolor-changing material. The hydrogel-forming composition includeseither a charged, hydrogel-forming polymer or a neutral,hydrogel-forming polymer. When a neutral, hydrogel-forming polymer isused, the hydrogel-forming composition also includes at least onecharged species, such as a charged polymer or charged particle.Therefore, the charged species is either a charged, hydrogel-formingpolymer, another type of charged polymer or a charged particle. Forexample, the hydrogel-forming composition can include a combination of acharged, hydrogel-forming polymer and a neutral hydrogel-formingpolymer. Hydrogel-forming compositions are used for a wide variety ofproducts, including hair gels. The hydrogel-forming compositions of theinvention desirably have a highly-charged element to bind strongly withan oppositely-charged colorant. The charged, hydrogel-forming polymersdesirably have low water solubility, but can be either dissolved orsuspended well in an aqueous solution or in a mixture of organic solventand water. The color-changing material is liquid at room temperature.When the color-changing material is applied to a surface, such as asubstrate, the color-changing material can be applied at roomtemperature (without heating) to form a hydrogel layer on the substrate.After the color-changing material is applied to a substrate, thevolatile solvent evaporates.

In another aspect, the present invention is directed to amultiple-component material. The multiple-component material includes asubstrate and a hydrogel-forming layer. The hydrogel-forming layerincludes a color-changing composition. The color-changing compositionincludes a hydrogel-forming composition having at least one chargedspecies, a charged colorant and a pH adjuster. The hydrogel-formingcomposition includes either a charged, hydrogel-forming polymer or aneutral, hydrogel-forming polymer. When the hydrogel-forming compositionincludes a neutral, hydrogel-forming polymer, the composition alsoincludes either a charged polymer or a charged particle. For themultiple-component material, the hydrogel-forming layer may be formed onthe substrate in one or more patterns selected from stripes, dots,geometric shapes, irregular shapes, alpha-numeric characters,anthropomorphic images, pictorial representation of animals, pictorialrepresentation of inanimate objects, cartoon characters, logos andtrademarks. The multiple-component material may be incorporated intovarious articles, including disposable absorbent articles such asincontinence garments. For example, the multiple-component material maybe incorporated into or form the outer cover of a disposable diaper. Inthis use as part of a disposable diaper, the multiple-component materialcan be used to indicate a change in the condition of the disposablediaper, such as the presence of urine or other waste. The chargedcolorant in the color-changing composition may be a pH indicator. Thecolor-changing compositions may include more than one charged colorant.

In another aspect, the present invention relates to a method of printingon a substrate. The method includes a step of providing a substrate tobe printed upon. The substrate may be a woven or a nonwoven material.The substrate may also be a laminate of a nonwoven material and a film,such as a polyolefin film. The method also includes a step of applyingan ink material onto the substrate. The ink material includes ahydrogel-forming composition having at least one charged species, acharged colorant, a pH adjuster and a volatile solvent. As the inkmaterial dries on the substrate, the volatile solvent evaporates and theremaining components of the ink material form a hydrogel layer on thesubstrate. The ink material is liquid at room temperature to permit easyapplication to the substrate. In addition to being printed on thesubstrate, the ink material may also be stamped on the substrate.

These aspects and additional aspects of the invention will be describedin greater detail herein. Further, it is to be understood that both theforegoing general description and the following detailed description areexemplary and are intended to provide further explanation of theinvention claimed.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure of the invention will be expressed in terms ofits various components, elements, constructions, configurations,arrangements and other features that may also be individually orcollectively be referenced by the term, “embodiment(s)” of theinvention, or other similar terms. It is contemplated that the variousforms of the disclosed invention may incorporate one or more of itsvarious features and embodiments, and that such features and embodimentsmay be employed in any desired, operative combination thereof.

It should also be noted that, when employed in the present disclosure,the terms “comprises”, “comprising” and other derivatives from the rootterm “comprise” are intended to be open-ended terms that specify thepresence of any stated features, elements, integers, steps, orcomponents, and are not intended to preclude the presence or addition ofone or more other features, elements, integers, steps, components, orgroups thereof.

The present invention relates to color-changing materials andmultiple-component materials that include a color-changing composition.Unlike prior art color-changing materials, the color-changing materialsof the present invention are either single-phase fluids or two-phaseparticle suspensions in a fluid. The color-changing materials andcolor-changing compositions include a solution medium, such as avolatile solvent, are liquid at room temperature and therefore, can beapplied to a substrate without heating. For example, the color-changingmaterials and color-changing compositions may be printed like an inkonto a substrate at room temperature. This feature of the color-changingmaterials and color-changing compositions makes them easier to handleduring the manufacture of the articles to which they are applied.Further, the color-changing materials and color-changing compositions ofthe present invention form a film when they are applied, such as byprinting, to a substrate and dried. A benefit of forming a film on thesubstrate is to afford good adherence and to prevent cracking.

The color-changing materials and color-changing compositions of theinvention are dissolved in a solution, such as a volatile solvent, as avehicle for the materials and compositions to be applied to a substratewhere the solvent portion of the solution evaporates after application.When they form a film-like hydrogel layer on a substrate (afterevaporation of the solvent), the color-changing materials andcolor-changing compositions of the invention are wettable but insolublein water. This feature makes the color-changing materials andcolor-changing compositions desirable for use in articles where thecompositions will be exposed to wetness. The feature also results incolor-changing materials and color-changing compositions that aredurable and that are resistant to leaching away from the substrates towhich they are applied. The hydrogel-forming layer may be formed on asubstrate in a desired pattern including stripes, dots, geometric shapesand irregular shapes and combinations of such pattern elements. Thehydrogel-forming layer may also be formed on the substrate as analpha-numeric character, an anthropomorphic image, a pictorialrepresentation of an animal, a pictorial representation of an inanimateobject, a cartoon character, a product or company logo and a trademarkor brand or combinations of such pictorial elements.

The present invention is directed to a color-changing material thatincludes a hydrogel-forming composition, a charged colorant, a pHadjuster and a volatile solvent. The hydrogel-forming compositionincludes at least one charged species, such as a charged,hydrogel-forming polymer and/or charged particles. The hydrogel-formingcomposition can include a charged, hydrogel-forming polymer by itself.When the hydrogel-forming composition includes a neutralhydrogel-forming polymer, the hydrogel-forming composition also includesa charged polymer or charged particle. The hydrogel-forming compositioncan also include a combination of a charged, hydrogel-forming polymerand a neutral hydrogel-forming polymer. Hydrogel-forming compositionsare used for a wide variety of products, including hair gels. Thehydrogel-forming compositions of the invention have the highly-chargedspecies to bind strongly with an oppositely-charged colorant. Thehighly-charged species can be the charged, hydrogel-forming polymer, thecharged particles or combinations of such polymers and particles.

The charged, hydrogel-forming polymers desirably have low watersolubility, but can be either dissolved or suspended well in an aqueoussolution or a mixture of organic solvent and water. The charged,hydrogel-forming polymers may be branched, linear or cross-linked andthey may be copolymers, such as block copolymers. The charged,hydrogel-forming polymers may be pre-formed or formed in situ fromcertain monomers. The in-situ formation of the charged, hydrogel-formingpolymers may be triggered by a number of techniques such as photoninduction and use of free radicals. Examples of suitable charged,hydrogel-forming polymers include poly(ethylene glycol)-grafted cationichydrogels (such as those described in the publication, K. Podual, F. J.Doyle III, and N. A. Peppas, Biomaterials, 21, 1439-1450, 2000); thecopolymer formed from 2-hydroxy methacrylate (HEMA) and methacrylamidepropyltrimethylammonium chloride; and dehydroxanthan gum (such as AMAZEXT film former commercially available from AkzoNobel). Additionalexamples of suitable charged, hydrogel-forming polymers include thecrosslinked cationic copolymer of vinylpyrrolidone (VP) and3-dimethylaminopropyl(meth)acrylamide (DMAPMA) monomer;(3-acrylamidopropyl)-trimethylammonium chloride (APTMAC1) monomercrosslinked with a neutral crosslinker (N,N-methylenebisacrylamide);crosslinked hydrophobically-modified dialkylallylammonium salts; vinylether of monethanolamine; and copolymerization of N,N,N,N-tetraallylpiperazinium dibromide (TAP) with N,N diallyl morpholinium bromide(DAM). The hydrogel-forming composition ranges from 5% to 50% of thecolor-changing material or the color-changing composition. If a charged,hydrogel-forming polymer is used in the hydrogel-forming composition,the polymer ranges from 5% to 50% of the hydrogel-forming composition.

Examples of suitable neutral, hydrogel-forming polymers includepolyethylene oxide, polyAMPS, polyvinylpyrrolidone, polyacrylamide,polyvinyl alcohol, sodium polyacrylate, agarose, methylcellulose andhylaronan. The neutral hydrogel-forming polymer can range from 5% to 50%of the hydrogel-forming composition.

Examples of suitable charged (either positively or negatively charged)particles include resin particles, including ion exchange resins such asREILLEX HPQ ion-exchange resin (a poly(4-vinylpyridine), cross-linked,methyl chloride quaternary salt) commercially available from ReillyIndustries, Inc. and sold through Sigma-Aldrich. Other examples ofcharged particles include latex particles made of polystyrenes andpolymethylacrylates that have surface functional groups to allowcovalent attachment of the charged colorants. Additionally, inorganicparticles such as clays and zeolites that allow absorption ofoppositely-charged charged colorants may be used as charged particles.The charged particles may be solid or porous. Charged particles that areporous may be desirable when it is necessary to absorb/adsorb a greaterquantity of charged colorant. The size of the charged particles mayrange from 10 nanometers to 10 micrometers and desirably from 200nanometers to 2 micrometers. The color-changing materials andcolor-changing compositions of the invention include charged particlesin an amount of from 0.1% to 10% of the total weight of thecolor-changing material or color-changing composition. Desirably, thecolor-changing materials and color-changing compositions of theinvention include charged particles in an amount of from 0.5% to 5% ofthe total weight of the color-changing material or color-changingcomposition.

Desirably, the charged particles have a large surface area on which thecharged colorant can be non-diffusively immobilized. The chargedcolorant may be covalently attached to or may be physically adsorbedonto the surface of the particles. The stable absorption of the chargedcolorant onto the charged particles increases the stability of thecharged colorant and reduces leaching of the charged colorant out of thecolor-changing material or color-changing composition.

In one aspect, the present invention is directed to a multiple-componentmaterial that includes a substrate and a hydrogel-forming layer. Thesubstrate may be in the form of a porous foam, a reticulated foam,cellulose tissues, a plastic film, a woven material or a nonwovenmaterial. Suitable plastic films that may be used to form the substrateinclude polyethylene films and polypropylene films. Suitable wovenmaterials include woven materials made from natural fibers, syntheticfibers or combinations of natural and synthetic fibers. Natural fibersinclude cotton, silk and wool fibers and synthetic fibers includepolyester, polyethylene and polypropylene fibers. Suitable nonwovenmaterials include nonwoven materials made through traditional techniquessuch as spunbond, meltblown and bonded carded web materials. Thespunbond, meltblown and bonded carded web materials may be made fromsuitable synthetic fibers such as polyester, polyethylene andpolypropylene fibers. The substrate may include combinations of thematerials identified above such as a substrate that includes both aporous foam and a nonwoven material or a substrate that includes both aplastic film and a nonwoven material.

The multiple-component materials of the invention also include ahydrogel-forming layer that is adhered to the substrate. Thehydrogel-forming layer includes a color-changing composition. Thecolor-changing composition includes a hydrogel-forming composition. Thehydrogel-forming layer is generally formed by drying the color-changingcomposition through solvent evaporation. The hydrogel-forming layer isgenerally thinner and film-like in relation to the thickness of thesubstrate. Because the color-changing compositions of the invention areliquid or are liquid suspensions at room temperature, they can beapplied through printing or stamping directly onto the substrate(thereby self-forming the hydrogel-forming layer). The hydrogel-formingcomposition may include either a charged, hydrogel-forming polymerand/or charged particles. When a neutral hydrogel-forming polymer isused in the composition, at least one charged polymer or chargedparticle is also included in the hydrogel-forming composition. Thehydrogel-forming composition can also include a combination of acharged, hydrogel-forming polymer and a neutral hydrogel-formingpolymer.

The color-changing materials and color-changing compositions of theinvention also include a charged colorant that may functionally act as apH indicator. When the hydrogel-forming composition includes a chargedparticle, the charged colorant is non-diffusively immobilized on thecharged particle. The charged colorant is “non-diffusively immobilized”on the charged particle when the presence of the charged colorant can bereproducibly measured and when the charged colorant is present insufficient amount to effectuate a change in color visible to the unaidedhuman eye when the color-changing material or color-changing compositionis exposed to a pH change (where the pH change would be sufficient tocause a change in color for the charged colorant by itself). The chargedcolorant may be a neutral pH indicator, a charged pH indicator or azwitterionic pH indicator. When the hydrogel-forming compositionincludes a charged particle, the charged colorant may be physicallyabsorbed through hydrophobic interactions or charge-charge interactions.The charged colorant is desirably oppositely charged to the chargedparticle for immobilization.

As a pH indicator, the charged colorant desirably has a color transitionpH at either greater than 9.5 or lower than 5.5. The color change may befrom color to colorless, colorless to color or from one color to anothercolor. The charged colorant has the charged functional groups either inthe core chromophore structure or derivatized as pendent groups of apolymer. Examples of suitable charged colorants include the following:gentian violet (methyl violet), leucomalachite green, methyl yellow,bromophenol blue, Congo red, methyl orange, malachite green, brilliangreen, crystal violet, erythrosin B, methyl green, methyl violet 2B,picric acid, napthol yellow S, quinaldine red, Eosin Y, basic fuchsin,4-(p-anilinophenylazo)benzene-sulfonic acid, sodium salt, phloxine B,bromochlorophenol blue W.S., ethyl orange, bromocresol nile blue A,thymolphthalein, aniline blue W.S., alizarin yellow GG, morgant orangeI, tropaeolin O, orange G, acid fuchsin, thiazol yellow G, indigocarmine, phenolphthalein, thymolphthalein, alizarine yellow R,bromocresol green and their respective derivatives. The color-changingmaterials and color-changing compositions of the invention include acharged colorant in an amount of from 0.05% to 10% of the total weightof the color-changing material or color-changing composition. Desirably,the color-changing materials and color-changing compositions of theinvention include a charged colorant in an amount of from 0.5% to 5% ofthe total weight of the color-changing material or color-changingcomposition. The color-changing materials and color-changingcompositions of the invention may include more than one chargedcolorant. One or more charged colorants that have visually differentcolors may be combined or charged colorants having the same visual colormay be combined.

In addition to the other components, the color-changing materials andcolor-changing compositions include a pH adjuster. The pH adjuster isany molecule or composition that may be used to control the pH of thecolor-changing material or color-changing composition. The pH adjustermay be an acid, a base or a combination of both such as would be foundwith a buffering composition. The pH adjuster is selected in conjunctionwith the choice of charged colorant to be used in the color-changingmaterial or color-changing composition. For example, if thecolor-changing material or color-changing composition includes a chargedcolorant that has a color transition point that occurs at a pH of lowerthan 5.5, the selected pH adjuster is desirably an acid to make the pHof the color-changing material or color-changing composition acidic. Ifthe color-changing material or color-changing composition includes acharged colorant that transitions color at a pH higher than 9.5, theselected pH adjuster is desirably a base to make the pH of thecolor-changing composition basic. Examples of suitable acid pH adjustersinclude organic acids, inorganic acids and polymeric acids; morespecifically, examples include citric acid, oxalic acid, tartaric acid,salicylic acid, palmitic acid and stearic acid. Examples of suitablebase pH adjusters include organic bases, inorganic bases and polymericbases; more specifically, examples include sodium hydroxide, sodiumcarbonate, sodium bicarbonate, sodium borate, potassium hydroxide,polymeric amines, dendrimeric amine and 1,3-pentanediamine. CombinationpH adjusters that have a buffering effect include acetic buffer, boratebuffer and carbonate buffer. Desirably, the pH of the combination pHadjuster is either greater than 10 or lower than 5. Typically, thecombination pH adjuster is in solution form and the concentration of thebuffer may range from about 0.01 milliMolar to about 1000 milliMolar anddesirably range from about 1 milliMolar to about 20 milliMolar,depending on the combination pH adjuster selected. The color-changingmaterials and color-changing compositions of the invention include a pHadjuster in an amount of from 0.001% to 10% of the total weight of thecolor-changing material or color-changing composition. Desirably, thecolor-changing material and color-changing compositions of the inventioninclude a pH adjuster in an amount of from 0.1% to 5% of the totalweight of the color-changing material or color-changing composition.

Benefits of the pH adjuster include stabilizing the charged colorantagainst premature color changes that may be caused by exposure to humidenvironments. For example, the pH adjuster is believed to maintain astable pH, such as a low pH environment with an acidic pH adjuster,around the charged colorant even when the color-changing material andthe hydrogel-forming layer of the multiple-component material areexposed to high humidities.

The color-changing materials and color-changing compositions of theinvention may also include a base material. The base material may be asmall molecule, a polymeric material or a mixture of small molecules andpolymers. Examples of suitable small molecule base materials includeglycols, including triglycerols and their derivatives. Examples ofsuitable polymeric materials that may be used as base materials includepolyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol,water-soluble derivatives of polyacrylates and polyacrylamides,poly(hydroxyethyl methacrylates), poly(hydroxylethyl acrylates),carboxymethyl cellulose, gelatin and gum Arabic. Another suitable basematerial for the color-changing materials and color-changingcompositions of the invention is a varnish base such as a nitrocellulosecompound based varnish or a phenolic-modified co-solvent-type polyamideresin-based varnish. The color-changing materials and color-changingcompositions of the invention may include a base material in an amountof from 1% to 50% of the total weight of the color-changing material orcolor-changing composition. It is believed that the base material mayhelp the stability of the color-changing materials and color-changingcompositions, such as by increasing the stability of the suspension ofthe charged particles, when the hydrogel-forming composition includescharged particles. It is also believed that the base material mayimprove the adhesion of the color-changing composition to the substrateof the multiple-component material. The base material may bewater-soluble or water-insoluble while the charged particles arewater-insoluble.

The color-changing materials of the invention include a volatile solventin addition to the hydrogel-forming composition, the charged colorantand the pH adjuster. With respect to the multiple-component materials ofthe invention, the components of the color-changing composition may beformed as the hydrogel-forming layer on the substrate. In this form, thecomponents of the color-changing composition must first be dissolved orsuspended in a solvent that later evaporates. The result of thecolor-changing composition forming a hydrogel-forming layer on thesubstrate is the multiple-component material of the invention. For boththe color-changing materials and the color-changing compositions of theinvention, the volatile solvent may be a single solvent or a mixture ofsolvents. Suitable solvents include water, ethanol, methanol, butanol,propanol, acetone, tetrahydrofuran and the mixtures of them. In makingthe color-changing materials and color-changing compositions of theinvention, the components may either be dissolved all together in thesolvent(s) or sequentially dissolved to make homogenous solutions. Whenthe color-changing materials and color-changing compositions include acharged particle, the charged particles may be suspended in the volatilesolvent.

An example of a useful application of the present invention is to applythe color-changing composition to a substrate that is used as acomponent of a disposable absorbent article. More specifically, thesubstrate may be a material that is used to form the outer cover of adisposable diaper. The substrate includes a polyolefin film such aspolyethylene film or polypropylene film that is used to form the outercover of a disposable diaper. The hydrogel-forming layer of the presentinvention may be formed on the substrate. Because the color-changingcompositions of the present invention are liquid at room temperature,they can be easily applied through printing to a substrate. Because theouter cover of an absorbent article, such as a disposable diaper, istypically adjacent to the absorbent structure of the article, thecolor-changing composition is applied to a component that is inproximity to the absorbent structure when the finished product is inuse. Therefore, the color-changing composition can be used to indicate achange in condition of the absorbent structure, such as wetness. Thecolor-changing compositions of the invention are water-wettable so thaturine can penetrate through the hydrogel-forming layer to cause thestructural and environmental change of the hydrogel-forming layer whichtriggers a rapid color change of the charged colorant component. Yet,the hydrogel-forming layer is water-insoluble to prevent leaching of thecharged colorant. These are desirable performance attributes. Thehydrogel-forming layer may include other components in addition to thecolor-changing composition.

In another aspect, the present invention relates to a method of printingon a substrate. The substrate may be a porous foam, a reticulated foam,cellulose tissues, a plastic film, a woven material or a nonwovenmaterial. The method includes a step of providing a substrate to beprinted upon. The substrate may be useful by itself or as a component ofanother useful article, such as an absorbent article. The method alsoincludes a step of applying an ink material onto the substrate. The inkmaterial includes a hydrogel-forming composition, a charged colorant, apH adjuster and a solvent. The ink material is liquid at roomtemperature and therefore, the ink material may be applied to thesubstrate at room temperature. The ink material may be applied onto thesubstrate in one or more patterns selected from stripes, dots, geometricshapes, irregular shapes, alpha-numeric characters, anthropomorphicimages, pictorial representation of animals, pictorial representation ofinanimate objects, cartoon characters, logos and trademarks. The inkmaterial may be applied by brush, printing nozzle or stamp.

The following are examples that illustrate aspects of the presentinvention:

Example 1

20 mg of hydrogel-forming polymer, Amaze XT from AkzoNobel, 4 mg ofmethacrylamide propyltrimethylammonium chloride, 0.5 ml of 10 mg/mloxalic acid and 1 ml of 2 mg/ml bromocresol green were added with 2 mlwater and 2 ml ethanol to form a mixture. The mixture was applied byspreading onto a piece of outer cover material from a disposable diaper.The outer cover material was a laminate of a spunbond nonwoven materialand a polyethylene film. The composition was applied onto thepolyethylene film. After the compositions were applied, they wereallowed to dry for 60 minutes. The composition remained yellow in coloras it dried. The composition adhered well to the outer cover materialand did not crack as it dried. When PBS buffer solution was applied tothe outer cover materials having the compositions, an instant colorchange from yellow to blue was observed. The intensity of the blue colorincreased as the PBS buffer solution was absorbed.

Example 2

Two color-changing materials were prepared and their re-gellation, colorchange and dye leaching were assessed upon exposure to phosphatebuffered saline. While the hydrogel-forming composition components weresampled from commercially-available hair gel products, when they werecombined with a charged colorant, pH adjuster and aqueous solvent, theyrepresented color-changing materials of the invention. About 1milliliter samples of each of the hydrogel-forming compositions (derivedfrom commercially-available hair gel products) were added to aneppendorf vessel and mixed with 100 microliters of a combination ofbromocresol green (0.2 mg/mL) and citric acid (5 mg/mL) in watersolution. Each representative color-changing material was yellow incolor and was applied to the outer cover material of a disposable diaperand left overnight to dry. The color-changing materials formed thinfilms on the outer cover material and remained yellow. Each film wasthen exposed to phosphate buffered saline (PBS) buffer. The third columnof the table below describes the observations for each film layer thatwas formed with respect to re-gellation, color change and dye leachingupon contact with PBS buffer.

Hair gel brand/Company Hydrogel-Forming Polymers Observations Set Me Up/Acrylate/Beheneth-25 Re-gelled, from yellow Herbal Essences methacrylatecopolymer to deep blue, minimal and Acrylate copolymer leachingFrizz-Ease/John Copolymer of vinyl acetate Re-gelled, from yellow FriedaCollection & vinylpyrrolidone to deep blue, no leaching

The color-changing materials described and evaluated above show thatcolor-changing materials and color-changing compositions of theinvention are capable of dramatic color change upon wetting, minimal dyeleaching and the ability to form a film-like layer on a polyolefinsheet.

Example 3

A color-changing material of the invention was prepared by combining 9.6grams of hair gel, Set Me Up from Herbal Essences (hydrogel-formingcomposition), 5 milliliters of 40 mg/mL citric acid and 4 milliliters of0.2 mg/mL bromocresol green. The color-changing material was spread on apiece of polyethylene film, such as would be used as a component of anouter cover of a disposable absorbent article. The color-changingmaterial was allowed to dry at room temperature. The resultingmultiple-component material (the combination of the color-changingmaterial on the polyethylene film) was used to replace a section ofouter cover film on a HUGGIES disposable diaper (newborn size). The sidewith the color-changing composition was positioned directly against theabsorbent core of the disposable diaper and held in position using tape.The disposable diaper was then insulted with 10 milliliters of PBSbuffer solution. After ten minutes, the color-changing compositionchanged color from greenish yellow to blue in response to the wetness.After one day, there was no visible leaching of the color away from theouter cover into the absorbent core. The strong blue color remainedthree days later.

While the color-changing materials and multiple-component materials ofthe invention have been described in detail with respect to specificaspects thereof, it will be appreciated that those skilled in the art,upon attaining an understanding of the foregoing, may readily conceiveof alterations to, variations of and equivalents to these materials.Accordingly, the scope of the present invention should be assessed asthat of the appended claims and any equivalents thereto.

1. A color-changing material comprising: a hydrogel-forming compositioncomprising a charged hydrogel-forming polymer, the hydrogel-formingcomposition containing at least one charged species; a charged colorant;a pH adjuster; and a volatile solvent; wherein the chargedhydrogel-forming polymer is selected from poly(ethylene glycol)-graftedcationic hydrogels; a copolymer of 2-hydroxyethyl methacrylate (HEMA)and methacrylamide propyltrimethylammonium chloride; a crosslinkedcationic copolymer of vinylpyrrolidone (VP) and3-dimethylaminopropyl(meth)acrylamide (DMAPMA) monomer;(3-acrylamidopropyl)-trimethylammonium chloride (APTMAC1) monomercrosslinked with a neutral crosslinker N,N-methylenebisacrylamide;crosslinked hydrophobically-modified dialkyldiallylammonium salts; avinyl ether of monoethanolamine; and copolymerization ofN,N,N,N-tetrallyl piperazinium dibromide (TAP) with N,N-diallylmorpholinium bromide (DAM).
 2. The color-changing material of claim 1,further comprising a neutral hydrogel-forming polymer selected frompolyethylene oxide, polyAMPS, polyvinylpyrrolidone, polyacrylamide,polyvinyl alcohol, sodium polyacrylate, agarose, methylcellulose andhylaronan.
 3. The color-changing material of claim 1, wherein thecolor-changing material includes more than one charged colorant.
 4. Thecolor-changing material of claim 1, wherein the charged colorant is a pHindicator having a color transition pH of greater than
 9. 5. Thecolor-changing material of claim 1, wherein the charged colorant is a pHindicator having a color transition pH of less than 5.5.
 6. Thecolor-changing material of claim 1, wherein the volatile solvent isselected from water, low alcohol, acetone, tetrahydrofuran and mixturesof these volatile solvents.
 7. A multiple-component material, thematerial comprising: a substrate, the substrate having ahydrogel-forming layer, wherein the hydrogel-forming layer includes acolor-changing composition, the color-changing composition comprising ahydrogel-forming composition comprising a charged hydrogel-formingpolymer; a charged colorant; a volatile solvent; and a pH adjuster;wherein the charged hydrogel-forming polymer is selected frompoly(ethylene glycol)-grafted cationic hydrogels; a copolymer of2-hydroxyethyl methacrylate (HEMA) and methacrylamidepropyltrimethylammonium chloride; a crosslinked cationic copolymer ofvinylpyrrolidone (VP) and 3-dimethylaminopropyl(meth)acrylamide (DMAPMA)monomer; (3-acrylamidopropyl)-trimethylammonium chloride (APTMAC1)monomer crosslinked with a neutral crosslinkerN,N-methylenebisacrylamide; crosslinked hydrophobically-modifieddialkyldiallylammonium salts; a vinyl ether of monoethanolamine; andcopolymerization of N,N,N,N-tetrallylpiperazinium dibromide (TAP) withN,N-diallyl morpholinium bromide (DAM).
 8. The multiple-componentmaterial of claim 7, wherein the hydrogel-forming composition comprisesa neutral, hydrogel-forming polymer.
 9. The multiple-component materialof claim 7, wherein the hydrogel-forming layer is formed on thesubstrate in one or more patterns selected from stripes, dots, geometricshapes, irregular shapes, alpha-numeric characters, anthropomorphicimages, pictorial representation of animals, pictorial representation ofinanimate objects, cartoon characters, logos and trademarks.
 10. Adisposable absorbent article including the multiple-component materialof claim
 7. 11. The multiple-component material of claim 7, wherein themultiple-component material is an outer cover material for a disposableabsorbent article.
 12. The multiple-component material of claim 7,wherein the color-changing composition includes more than one chargedcolorant.
 13. The multiple-component material of claim 7, wherein thesubstrate is a non-woven material.
 14. The multiple-component materialof claim 7, wherein the substrate is a polyolefin film.
 15. Themultiple-component material of claim 14, wherein the polyolefin film isselected from a polyethylene film and a polypropylene film.
 16. A methodof printing on a substrate, comprising the steps of: providing asubstrate to be printed upon; and applying an ink material onto thesubstrate, wherein the ink material includes a hydrogel-formingcomposition comprising a charged hydrogel-forming polymer, thehydrogel-forming composition containing at least one charged species; acharged colorant; a pH adjuster; and a volatile solvent; wherein thecharged hydrogel-forming polymer is selected from poly(ethyleneglycol)-grafted cationic hydrogels; a copolymer of 2-hydroxyethylmethacrylate (HEMA) and methacrylamide propyltrimethylammonium chloride;a crosslinked cationic copolymer of vinylpyrrolidone (VP) and3-dimethylaminopropyl(meth)acrylamide (DMAPMA) monomer;(3-acrylamidopropyl)-trimethylammonium chloride (APTMAC1) monomercrosslinked with a neutral crosslinker N,N-methylenebisacrylamide;crosslinked hydrophobically-modified dialkyldiallylammonium salts; avinyl ether of monoethanolamine; and copolymerization ofN,N,N,N-tetrallyl piperazinium dibromide (TAP) with N,N-diallylmorpholinium bromide (DAM).
 17. The method of claim 16, wherein the inkmaterial is applied at room temperature.
 18. The method of claim 16,wherein the ink material is applied onto the substrate in one or morepatterns selected from stripes, dots, geometric shapes, irregularshapes, alpha-numeric characters, anthropomorphic images, pictorialrepresentation of animals, pictorial representation of inanimateobjects, cartoon characters, logos and trademarks.